1. Field of the Invention
The present invention relates to an imaging lens for copying, and a copying apparatus such as copier, platemaker, or the like using this imaging lens for copying; and, in particular, to an imaging lens for copying and a copying apparatus, having a refractive index distribution type lens, used for reading out images at a magnification near 1:1.
2. Description of the Prior Art
Conventionally known as an imaging lens used in a copying apparatus such as facsimile machine, image scanner, or the like is that of a three-sheet configuration having a refractive index distribution type lens (Japanese Unexamined Patent Publication No. 7-294804).
The imaging lens disclosed in the above-mentioned publication comprises, successively from the object side, a first lens made of a positive meniscus lens having a convex surface directed onto the object side, a second lens made of a biconcave lens, and a third lens made of a biconvex lens, in which at least one lens is a refractive index distribution type lens, thereby being capable of achieving wider angle of view and higher performances and making the whole lens compact.
The imaging lens disclosed in the above-mentioned publication, however, is aimed at reducing an original image to about 1/10 and forming thus reduced image onto a solid-state imaging device such as CCD. Therefore, it is not so suitable for reading out images at a magnification near 1:1, which is the most important in the copier, platemaker, and the like. Hence, when used for reading an image at a magnification near 1:1, various kinds of aberration become very large in the read-out image.